Short communication
ZrOCl2/nano TiO2 as an Efficient Catalyst for the One Pot Synthesis of Naphthopyranopyrimidines Under Solvent-free Conditions
Mahboubeh Mohaqeq,1 Javad Safaei-Ghomi,1* and Hossein Shahbazi-Alavi2
1 Department of Chemistry, Qom Branch, Islamic Azad University, Qom, I. R. Iran
2 Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317-51167, I. R. Iran
* Corresponding author: E-mail: safaei@kashanu.ac.ir, Telefax: +983155912385
Received: 29-03-2015
Abstract
ZrOCl2/nano-TiO2 has been used as an efficient catalyst for the preparation of naphtho[1',2':5,6]pyrano[2,3-d]pyrimidi-ne derivatives by the three-component reaction of aldehydes, ß-naphthol and 1,3-dimethylbarbituric acid. The advantages of the reaction are solvent-free conditions, short reaction times, easy workup, good to excellent yields, and cost-effective and reusable catalyst.
Keywords: ZrOCl2/nano-TiO2, heterogeneous catalyst, naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine, one-pot reaction, solvent-free
1. Introduction
Pyrans belong to an important class of compounds which show a wide range of biological activities.1 The pyranopyrimidines exhibit important biological properties such as anticancer,2 antitubercular activity (against Myco-bacterium tuberculosis H37Rv [ATCC-27294]), antifungal (against Aspergillus niger [MTCC-282]3) and antibacte-rial4 activities. Naphthopyranopyrimidines are fused hete-rocyclic compounds that display antioxidant5 and antimi-crobial6 activities. Therefore, the development of simple methods for their synthesis is an important challenge. Undoubtedly, the synthesis of naphthopyranopyrimidines through multicomponent reactions (MCRs) has been paid much attention due to excellent synthetic efficiency, inherent atom economy, procedural simplicity and environmental friendliness.7-11 The eco-friendly, solvent-free multicomponent approach opens up numerous possibilities for environmentally clean synthesis which involves reduction or elimination of the use or generation of hazardous chemicals.12-13 The possibility of performing multi-component reactions under solvent-free conditions with a heterogeneous catalyst could improve their cost-effectiveness and ecological acceptability.
Nanoparticles exhibit good catalytic activity due to their high surface-to-volume ratio in comparison to their heterogeneous counterparts. Separation of the catalyst and final product from the reaction mixture is one of the most important aspects of synthetic protocols. Nanopar-ticles decrease reaction times, impart greater selectivity and can be easily recovered from the reaction mixture by simple filtration.14-19 Utilizing binary supporting catalysts is a vast challenging necessity for organic chemists due to their expanding surface area. In comparison with conventional supports like solid-phase, nanoparticu-lar matrixes have a higher catalyst loading capacity owing to their very large surface area. Nano-TiO2 has been extensively used as a heterogeneous catalyst in many reactions due to its high activity, simple availability, non-toxicity, reusability, Lewis acid activity and long-term stability.20 Meanwhile, ZrOCl2.8H2O owing to its low to-xicity, commercial availability and moisture stability have gained much attention in organic synthesis.21 According to the above results we modified nano-TiO2 surfaces using ZrOCl2 for the synthesis of naphthopyranopyrimi-dines. Recently, the synthesis of naphthopyranopyrimidines has been reported using MCRs in the presence of diverse catalysts including iodine,22 InCl3,23 heteropolya-
Al(H2PO4)325 and P2O5.26 Herein, we report the use 2 as an efficient catalyst for the
cid2 Al(H PO ) and P O
ыи	auu i ^5
of ZrOCL/nano-TiO
synthesis of naphthopyranopyrimidines by the three-component reaction of aldehydes, ß-naphthol and 1,3-di-methylbarbituric acid under solvent-free conditions at 100 °C (Scheme 1).
Scheme 1. Three-component reaction of aldehydes, ß-naphthol and 1,3-dimethylbarbituric acid catalyzed by ZrOCl2/nano-TiO2
2. Results and Discussion
Figure 2. SEM image of ZrOCl2/nano-TiO2.
The powder XRD pattern for ZrOCl2 supported na-no-TiO2 catalyst is shown in Figure 1. In order to study the morphology and particle size of ZrOCl2 supported nano-TiO2, SEM image was also obtained (Figure 2), which shows particles with diameters in the range of nanometers.
Table 1. The model reaction carried out by various catalysts under solvent-free conditions at 100 °C a
Figure 1. The XRD pattern of ZrOCl2/nano-TiO2.
Initially, we focused on systematic evaluation of different catalysts in the reaction of 4-nitrobenzaldehyde, ß-naphthol and 1,3-dimethylbarbituric acid as a model reaction. Under solvent-free conditions, we were searching for the best reaction conditions in which 3 mol% of ZrOC-l2/nano-TiO2 catalyst gave excellent yields of product and an excessive amount of catalyst did not increase the yields significantly (Table 1).
Entry	Catalyst	mol%	Time(min)	Yieldb%
1	CH3COOH	10	66	10
2	Na2SO4	15	100	35
3	H2SO4	3	35	20
4	Montmorillonite	5	60	12
5	^-TSA	5	50	60
6	CuO	5	60	30
7	Ethylene glycol	10	60	25
8	ZrOCl2/nano-TiO2	1	25	80
9	ZrOCl2/nano-TiO2	3	25	85
10	ZrOCl2/nano-TiO2	6	25	85
a 4-nitrobenzaldehyde (1.1 mmol), ß-naphthol (1 mmol) and 1,3-di-methylbarbituric acid ( 1 mmol) b Isolated yield.
Investigations of the reaction scope revealed that various aromatic aldehydes bearing electron-withdrawing and electron-donating groups can be utilized in this protocol (Table 2).
The proposed mechanism for this three-component reaction is outlined in Scheme 2. ß-naphthol undergoes condensation with aldehyde in presence of ZrOCl2/nano-TiO2 to afford a,ß-unsaturated carbonyl compound I. Michael addition reaction between compounds I and 1,3-dimethylbarbituric acid gives intermediate II followed by cyclodehydration which gives the desired naphthopyra-nopyrimidine.
The recycling of ZrOCl2 supported nano-TiO2 catalyst was also examined and results are summarized in Table 3. The recovered catalyst was washed by hot etha-nol (3 X 5 mL) then dried at 80 °C and used in the next run. The results showed that the catalyst could be reused several times without noticeable loss of catalytic activity.
Table 2. Synthesis of naphtho[1',2':5,6]pyrano[2,3-rf]pyrimidine by ZrOCl2/nano-TiO2 under solvent-free conditions at 100 °C.
Entry
4a-i	aldehyde
Product
Time (min)	Yield%a	mp °C (ref)
4a
4b
4c
4d
4e
4f
4g
4h
4i
28
25
30
27
27
31
25
27
28
82
85
81
83
84
80
84
82
82
243-24522
291-293 '
223-225 22
274-276
305-307
200-202 2
219-221
310-3122
222-224 22
a Isolated yield.
1
2
3
4
5
6
7
8
9
Scheme 2: The proposed reaction pathway for the synthesis of naphthopyranopyrimidine catalyzed by ZrOCl2/nano-TiO2.
Table 3. Recycling of ZrOCl2/nano-TiO2 catalyst in the preparation of 4b.
Run	1 2	3 4 Г
Yield (%)a 85	84	84	83	82
a Isolated yield.
3. Experimental
3. 1. General
The products were isolated and characterized by physical and spectral data. :H NMR and 13C NMR spectra were recorded on Bruker Avance-400 MHz spectrometers in the presence of tetramethylsilane as internal standard. The IR spectra were recorded on FT-IR Magna 550 apparatus using KBr plates. Melting points were determined on Electro thermal 9200, and are not corrected. The elemental analyses (C, H, N) were obtained from a Carlo ERBA Model EA 1108 analyzer. X-ray powder diffraction (XRD) was carried out on a Philips diffractometer of X'pert company at X = 1.5406 À. Microscopic morphology of products was visualized by SEM LEO 1455VP.
3. 2. Preparation of ZrOCl2 Supported Nano-TiO2 Catalyst
In a typical procedure, nano-TiO2 (1 g) and ZrOCl2 (0.3 g) were combined and stirred for 24 h at room temperature in CH2Cl2. Afterwards, The solid was dried at 80 °C for 24 h. Then, the solid was calcinated at 300 °C for 30 min.
3. 3. General Procedure for the Synthesis of Naphthopyranopyrimidines (4a-i):
To a mixture of aldehyde (1.1 mmol), ß-naphthol (1.0 mmol), and 1,3-dimethylbarbutyric acid (1.0 mmol), 3 mol% of ZrOCl2/nano-TiO2 were added as the catalyst, and the mixture was stirred for an appropriate time at 100 °C in an oil bath. After completion of the reaction, indicated by TLC, the reaction mixture was dissolved in the appropriate volume of hot ethanol, stirred for 5 min, filtered, and the heterogeneous catalyst recovered. Solution with product was concentrated and recrystallized from ethanol to get pure compound.
3. 4. Analytical Data:
12-(4-Bromophenyl)-8,10-dimethyl-8,12-dihydro-9#-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10tf)-dione (4a): White solid; mp 243-245 °C; IR (KB-r): vmax 2921, 2852, 1665, 1643, 1593, 1483, 1226, 506 cm-1; aH NMR (CDCl3, 400 MHz): 5 (ppm) 3.42 (s, CH3, 3H), 3.49 (s, CH3, 3H), 5.88 (s, CH, 1H), 7.04-7.35 (m, 5H), 7.41 (d, J =3 8.5 Hz, 1H), 7.45-8.04 (m, 4H); 13C NMR (CDCl3, 100 MHz): 5 (ppm) 28.3, 29.0, 35.5, 90.8, 116.2, 116.6, 120.6, 123.7, 125.6, 127.5, 128.5, 129.7, 130.0, 130.7, 131.5, 131.7, 142.8, 147.1, 150.5, 152.2, 161.9; Anal.Calcd.for C23H17BrN2O3: C, 61.48; H, 3.81; N, 6.23. Found C, 61.39; H, 3.75; N, 6.19.
8,10-Dimethyl-12-(4-nitrophenyl)-8,12-dihydro-9#-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10tf)-dione (4b): Cream solid; mp 290-292 °C, IR (KB-r): vmax 2921, , 1667, 1595, 1513, 1342, 1229, 1175 cm-1; 1H NMr (CDCl3, 400 MHz): 5 (ppm) 3.48 (s, CH3, 3H), 3.63 (s, CH3, 3H), 5.91 (s, CH, 1H), 7.26 (m, 5H), 7.60 (m, 2H), 8.07 (d, J = 8.8 Hz, 1H), 8.32 (d, J = 8.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz): 5 (ppm) 28.3, 29.1, 36.0, 90.0, 115.7, 116.3, 123.3, 123.7, 125.8, 127.8, 128.7, 129.2, 130.2, 130.5, 131.8, 146.5, 147.1, 150.4, 150.8, 152.4, 161.8; Anal.Calcd.for C23H17N3O5: C, 66.50; H, 4.12; N, 10.12; Found C, 66.41; H, 4.02; NN, 10.20.
8,10-Dimethyl-12-phenyl-8,12-dihydro-9#-napht-ho[1',2':5,6]pyrano[2,3-rf]pyrimidine-9,11-(10#)-dio-ne (4c): White solid; mp 223-225 ° C, IR (KBr): vmax 2921, 2849, 1669, 1645, 1593, 1485, 1234, 1175 cm-1, mH NMR (CDCl3, 400 MHz): 5 (ppm) 3.34 (s, CH3, 3H), 3.59 (s, CH3, 3H), 5.77 (s, CH, 1H), 7.12-7.50 (m, 8H), 7.82 (m, 2H), 7.96 (m, 1H); 13C NMR (CDCl3, 100 MHz): 5 (ppm) 28.2, 29.1, 35.9, 91.4, 116.2, 117.3, 123.9, 125.4,
126.7,	127.4, 128.2, 128.4, 129.0, 129.5, 130.9, 131.7,
143.8,	147.1, 150.6, 152.2, 161.9; Anal.Calcd.for C23H18N2O3: C, 74.58; H, 4.90; N, 7.56; Found C, 74.62; H, 4.96; N, 7.48.
12-(4-chlorophenyl)-8,10-dimethyl-8,12-dihydro-9#-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-
(10H)-dione (4d): White solid; mp 275-277 °C; IR (KB-r): vmax 2961, 1668, 1622, 1358, 1205 cm-1, 1H NMR (CDCl* 400 MHz): 5 (ppm) 3.33 (s, CH3, 3H), 3.60 (s, CH3, 3H), 5.75 (s, CH, 1H), 7.18 (d, J = 8Hz, 2H), 7.28 (d, J = 8Hz, 2H), 7.32 (m, 1H), 7.48 (m, 2H), 7.75-7.90 (m, 2H), 8.12 (d, J = 8Hz, 1H); 13C NMR (CDCl3, 100 MHz): 5 (ppm) 28.2, 29.0, 35.4, 90.8, 116.3, 116.7, 123.7, 125.6, 127.5, 128.5, 129.6, 129.7, 130.7, 131.7, 132.5, 142.3, 147.1, 150.5, 152.2, 161.9; Anal.Calcd.for C23H17ClN2O3: C, 68.23; H, 4.23; N, 6.92; Found C, 68.16; H, 4.16; NN, 6.96.
12-(4-fluorophenyl)-8,10-dimethyl-8,12-dihydro-9H-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10H)-dione (4e): White solid; mp 300-303 °C, IR (KB-r): vmax 2955, 1664, 1631, 1342, 1203, 1164 cm1, 1H NMR(CdC13, 400 MHz): 5 (ppm) 3.33 (s, CH3, 3H), 3.62 (s, CH3, 3H), 5.75 (s, CH, 1H), 6.88 (m, 2H), 7.25-7.37 (m, 3H), 7.41 (m, 2H), 7.75-7.89 (m, 3H); 13C NMR (CDC13, 100 MHz): 5 (ppm) 28.2, 29.1, 35.3, 91.2, 115.4,
116.3,	117.0, 123.8, 125.6, 127.5, 128.6, 129.6, 129.7,
129.8,	130.7, 131.8, 139.6, 147.1, 150.6, 152.2, 161.9; Anal.Calcd.for C23H17FN2O3: C, 71.13; H, 4.41; N, 7.21; Found C, 71.19; 121, 4.35; N, 7.16.
8,10-Dimethyl-12-p-tolyl-8,12-dihydro-9H-napht-ho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10H)-dione (4f): White solid; mp 200-202 °C, IR (KBr): vmax 2919, 2853, 1700, 1638, 1486, 1229, 1172 cm-1; ^H NMR (CDC13, 400 MHz): 5 (ppm) 2.24 (s, 3H), 3.32 (s, CH3, 3H), 3.58 (s, CH3, 3H), 5.71 (s, CH, 1H), 6.96 (d, J = 8Hz, 2H), 7.15 (d, J =3 8Hz, 2H), 7.45 (m, 3H), 7.66 (m, 2H), 7.94 (m, 1H); 13C NMR (CDC13, 100 MHz): 5 (ppm) 21.1, 28.1, 29.0, 35.5, 91.6, 116.2, 117.7, 124.3, 125.4, 127.4, 128.1, 128.4, 129.2, 129.3, 130.1, 131.7, 136.0, 140.9, 147.1, 150.3, 151.8, 161.5; Anal.Calcd.for C24H20N2O3: C, 74.98; H, 5.24; N, 7.29; Found C, 75.05; H, 5.31; N, 7.21.
12-(2,4-dichlorophenyl)-8,10-dimethyl-8,12-dihydro-9H-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10H)-dione (4g): White solid; mp 219-221 °C, IR (KB-r): vmax 2923, 1642, 1582, 1484, 1174, 743, 718 cm-1; 1H NMR XCDC13, 400 MHz): 5 (ppm) 3.30 (s, CH3, 3H), 3.64 (s, CH3, 3H), 5.98 (s, CH, 1H), 7.1 (m, 1H), 7.22 (s, 1H), 7.33 (m, 2H), 7.53 (m, 2H), 7.80 (m, 2H), 8.10 (m, 1H); 13C NMR (CDC13, 100 MHz): 5 (ppm) 28.1, 29.0, 33.8, 89.9, 116.2, 123.7, 125.5, 127.4, 127.6, 128.6, 129.6,
129.9,	130.9, 131.5, 132.3, 133.0, 133.7, 139.7, 146.8,
150.4,	152.4, 161.5; Anal.Calcd.for C23H16Cl2N2O3: C, 62.88; H, 3.67; N, 6.38; Found C,62.79; H, 3.61; NN, (5.29.
8,10-Dimethyl-12-(3-nitrophenyl)-8,12-dihydro-9H-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10H)-dione (4h): Cream solid; mp 307-309 °C, IR (KB-r): vmax 2953, 1688, 1645, 1583, 1545, 1483 cm1; 1H NMR (CDC13, 400 MHz): 5 (ppm) 3.39 (s, CH3, 3H), 3.71
(s, CH3, 3H), 5.95 (s, CH, 1H), 7.55-7.85 (m, 8H), 8.10 (m, 1H), 8.14 (s, 1H); 13C NMR (CDC13, 100 MHz): 5 (ppm) 28.2, 29.1, 36.0, 90.0, 115.5, 116.1, 123.2, 123.7, 125.4, 127.6, 128.4, 128.7, 129.0, 130.1, 130.3, 131.5, 143.2, 146.4, 147.0, 150.2, 150.8, 152.3, 161.5; Anal.Calcd.for C23H17N3O5: C, 66.50; H, 4.12; N, 10.12; Found C, 66.41; H, 4.07; N5, 10.20.
12-(3-chlorophenyl)-8,10-dimethyl-8,12-dihydro-9H-naphtho[1',2':5,6]pyrano[2,3-d]pyrimidine-9,11-(10H)-dione (4i): White solid; mp 222-224 °C, IR (KBr): vmax 2921, 1639, 1588, 1478, 1424 cm1; 1H NMR (CDC-13, 4Ю0 MHz): 5 (ppm) 3.33 (s, CH3, 3H), 3.61 (s, CH3, 3H), 5.75 (s, CH, 1H), 7.15-7.60 (m, 7H), 7.81-7.92 (m, 3H); 1H NMR (CDC13, 400 MHz): 5 (ppm); 28.2, 29.1, 35.8, 90.8, 116.3, 116.5, 123.7, 125.6, 126.7, 127.0,
127.6,	128.2, 128.6, 129.5, 129.8, 130.7, 131.8, 134.3,
145.7,	147.1, 150.5, 152.3, 161.8; Anal.Calcd.for C23H17ClN2O3: C, 68.23; H, 4.23; N, 6.92; Found C, 68Л8; H, 4.12; N, 6.85.
4. Conclusions
In summary, we have developed the synthesis of naphtho[r,2':5,6]pyrano[2,3-d]pyrimidines in the presence of ZrOCl2/nano-TiO2 as an efficient catalyst under solvent-free conditions. The procedure offers several advantages including easy workup, the employment of a cost-effective catalyst, short reaction times, excellent yields and reusability of the catalyst. Furthermore, synthesized compounds provide promising candidates for chemical biology and drug discovery.
5. Acknowledgements
The authors acknowledge a reviewer who provided helpful insights and are grateful to Islamic Azad University, Qom Branch for supporting this work.
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Povzetek
V prispevku je opisana uporaba ZrOCl2/nano-TiO2 kot učinkovitega katalizatorja za pripravo nafto[1',2':5,6]pira-no[2,3-d]pirimidinskih derivatov v trikomponentni reakciji med aldehidi, yö-naftolom in 1,3-dimetilbarbiturno kislino. Prednosti tako izvedenih reakcij so izključitev topila med potekom reakcije, kratki reakcijski časi, enostavna izolacija produkta, dobri izkoristki reakcij ter možnost reciklaže relativno cenenega katalizatorja.